CRYPTOGAMS 



297 



Fig. 425. — A sea- 

 weed with broad, ex- 

 panded thallus. 



Beginning with the simplest forms, cryptogams are grouped 

 in three great orders : — 



333. I. Thallophytes, or thallus plants. — This group takes 

 its name from the thallus structure that characterizes its 

 vegetation. In its typical form, a thallus is 

 a more or less fiat, expanded body, of which 

 the lichens and liverworts offer familiar ex- 

 amples among land plants, and the kelps and 

 laminarias among seaweeds. It may be of 

 any size and shape, however, and sometimes ^ 

 consists of a mere filament, as in the com- 

 mon brook silk, or even of a single cell (Fig. 

 429) . The term is applied in general to the 

 simplest kinds of vegetable structure, in 

 which there is no differentiation of tissues, 

 and no true distinction of root, stem, and 

 leaves. While it is not peculiar to the thal- 

 lophytes, it has attained its most typical development among 

 them, and the name is therefore retained as distinctive of 

 that group. It embraces two great divi- 

 sions, the Algae and Fungi. The first 

 includes seaweeds and the common fresh- 

 water brook silks and pond scums, be- 

 sides numerous microscopic forms whose 

 presence escapes the eye altogether, or is 

 made known only by the discolorations 

 ( ^ and other changes caused by them in the 



KjL^^-^^ water. To the fungi belong the mush- 



FiG. 426.— AnthocG- Tooms and puffballs, the molds, rusts, 



ros, a liverwort with flat, niildcWS, and the vast tribe of micro- 

 spreading thallus. . . 11 1 7 • 1-1 



scopic organisms called haderia, which 

 are so active in the production of fermentation, putrefac- 

 tion, and disease. 



334. n. Bryophytes, or moss plants. — This group likewise 

 contains two main divisions, Mosses and liverworts. Famil- 

 iar examples of the latter are the flat, spreading green plants, 



